"That was the hardest scene I've ever had to write," the author told Entertainment Weekly. "It was like murdering two of your children.

"I try to make the readers feel they've lived the events of the book. Just as you grieve if a friend is killed, you should grieve if a fictional character is killed. You should care. If somebody dies and you just go get more popcorn, it's a superficial experience isn't it?"

Martin added that he knew "almost from the beginning" that Robb and Catelyn would die, explaining that it helped Game of Thrones remain "unpredictable".

"I killed Ned [Sean Bean] because everybody thinks he's the hero and that, sure, he's going to get into trouble, but then he'll somehow get out of it," he said.

"The next predictable thing is to think his eldest son [Robb] is going to rise up and avenge his father. And everybody is going to expect that. So immediately [killing Robb] became the next thing I had to do."

Richard Madden previously described filming his final scenes on Game of Thrones as a "big, emotional moment".